[blucar]

From my prospective, based on many applications of PCV systems on pre "SMOG" engines that I have done, I have formed the opinion that very few people really have a clear grasp on how a Positive Crankcase Valve system works.
The object of a PCV system is to draw clean, filtered air into the engine, circulated it through the engine, utilizing engine vacuum, then introduce the oil contaminated air into the intake system where it is blended with the air/fuel mixture and is burned off.
The introduction of the PCV system in 1963, eliminate 90% of the "SMOG" vapors that the internal combustion engines emitted via the open road draft devise (s) that had been in use since the invention of the internal combustion engine.
Many years ago I encountered the PCV system that Ford used on the '64 Y-Blocks. This system used a little dome shaped cap that replaced the '63 and earlier road draft tubes, the cap had a fitting for a 3/8" hose, the hose was attached to a PCV that was threaded into the intake manifold.
Air was drawn into the crankcase via the filtered oil fill cap, the vacuum then pulled the air flow through the block/valve chamber and into the intake manifold, to be burned off.. No blow by, no crankcase pressure, just a well ventilated clean engine.
GM used a variation of the same domed adapter to eliminate the road draft tubes on the '63 SBC's, the only difference was GM used a PCV that plugged into a valve cover via a rubber grommet.
Some Y-Blocks have a crankcase breather on the lower left side of the block, this could be compared to the pan breather on the left side of many of the early flathead engine.. The block/pan breather has to be blocked off in order for a PCV to work properly.
OK now the problem is, how do you utilize a simple system like the Y-Blocks? Very simple, don't try to reinvent the wheel, and don't over engineer the system.
The 8BA/8CM engines are the easiest, eliminate the road draft tube from the front of the engine, fabricate something to take it's place to which a 3/8" hose can be attached. Find a good vacuum source, below the throttle plate (s).. Use a PCV that is from an engine that is close to the CID of the engine being modified.
From my way of thinking the system would work best if the air was drawn in from the rear of the engine, maybe via a modified early V8 modified fuel pump stand with a filtered cap on top.
I would think that if the vacuum is pulling vapors from the block via the old road draft port, and the original oil fill pipe was left open, circulation of the vapors would not be good.. Ya know the shortest distance between two points..
The early flatheads are more of a challenge because of the intake manifold would require drilling and threading of a hole that the PCV could be threaded into, then a vacuum source has to be obtained..
The WWII military vehicles used a closed crankcase, i.e. PCV because many of them were equipped to keep water out of the engine, because they "forded" water deeper than the engines, the breathers were extended to above the windshield, and/or they were intended for desert use in extremely dusty conditions...